verify Amazon SNS message

gistfile1.py

def verify(message):
  # the string to sign
  sign_str = []
  for key in ("Message", "MessageId", "Subject", "Timestamp", "TopicArn", "Type"):
    if key == "Subject" and key not in message:
      continue
    sign_str.append(key)
    sign_str.append(message[key])
  sign_str.append("")
  sign_str = "¥n".join(sign_str)
  
  # certificate file
  from Crypto.PublicKey import RSA
  cert = open('aws_sns.pem').read()
  rkey = RSA.importKey(cert)
  
  # verify
  from Crypto.Hash import SHA
  from Crypto.Signature import PKCS1_v1_5
  signature = base64.standard_b64decode(message["Signature"])
  h = SHA.new(sign_str)
  p = PKCS1_v1_5.new(rkey)
  valid = p.verify(h, signature)
  return valid